TMZ broke the story ... Nia was charged with misdemeanor battery by the Broward County State Attorney's Office after she pimp slapped the S**t out of co-star Jennifer Williams -- and it was all caught by VH1's cameras.

Nia faced up to a year in jail, but decided to strike a deal with prosecutors (good idea considering the whole "on tape" thing) ... and pled no contest.

In exchange she was sentenced to the following: 1-year probation, $645 fine, and ordered to write a letter of apology, stay away from Jennifer and undergo 13 weeks of anger management.